Spread-spectrum techniques are widely used in many modern day communication technologies (e.g., CDMA). Such techniques allow a signal to be spread over a large frequency, such that the signal's frequency bandwidth is increased (i.e., “spread” in the frequency domain). For example, direct sequence spread-spectrum operates to spread a digital radio frequency (RF) carrier signal's bandwidth by multiplying (i.e., modulating) digital data being transmitted by a pseudorandom sequence of digital values (e.g., “1” and “−1”) generated by a pseudorandom sequence generator. Multiplication of the digital data at a frequency much higher than that of the original carrier signal spreads the energy of the original carrier signal into a much wider frequency bandwidth. Such higher bandwidths allow for multiple signals to be transmitted at the same time, wherein each signal uses a different pseudorandom sequence.
To synchronize the digital transmission operations between a receiver and a transmitter a correlation unit may be used to recover data from a received signal (i.e., to determine whether a logic “1” or “0” was received). The correlation unit reconstructs (i.e., “de-spreads”) the original date, at the receiving end, by multiplying it by the same pseudorandom sequence of digital values. If the received signal matches the receiver's pseudorandom sequence then the correlation function is high and the system can extract that signal. If the receiver's pseudorandom sequence has nothing in common with the received signal, the correlation function is low (thus eliminating the signal). For example, a receiver may correlate a received signal with a known pseudorandom sequence generated by its own sequence generator. When a large positive correlation results between the received signal and the pseudorandom sequences, a “1” is detected, while when a large negative correlation results, a “0” is detected.